Method of preparing iodosilanes and compositions therefrom

ABSTRACT

Provided are complexes useful in the conversion of chloro- and bromo-silanes to highly desired iodosilanes such as H 2 SiI 2  and HSiI 3 , via a halide exchange reaction. The species which mediates this reaction is an iodide reactant comprising aluminum.

FIELD OF THE INVENTION

This invention belongs to the field of chemistry. It relates to methodology for preparing certain iodosilanes from the corresponding chloro- or bromo-silanes using an aluminum-mediated halide exchange process.

BACKGROUND OF THE INVENTION

Halosilanes are useful as precursors in the manufacturing of microelectronic devices. In particular, halosilanes such as H₂SiI₂ and HSiI₃ are useful as precursor compounds for the deposition of silicon-containing films used in the manufacture of microelectronic devices. Current solution-based synthetic methodology describes the synthesis of H₂SiI₂ and other select iodosilanes from i) aryl silanes (Keinan et al. J. Org. Chem., Vol. 52, No. 22, 1987, pp. 4846-4851; Kerrigan et. al. U.S. Pat. No. 10,106,425 or ii) halosilanes such as SiH₂Cl₂ (U.S. Pat. No. 10,384,944).

Keinan et al. describe a synthetic method towards SiH₂I₂ formation that employs stoichiometric treatment of Phenyl-SiH₃, an arylsilane, with iodine in the presence of a catalyst such as ethyl acetate. The reaction by-products are the aromatic function from the arylsilane, liberated as benzene, and a complicated by-product mixture resulting from ethyl acetate decomposition. Tedious separation of the reaction by-products from the desired SiH₂I₂ complicates the process. In addition, arylsilane-based methods for preparing halosilanes typically generate product contaminated with iodine and/or hydrogen iodide, which are deleterious to the desired iodosilane product, so often antimony, silver, or copper are utilized to stabilize the iodosilane product.

U.S. Pat. No. 10,106,425 teaches the use of an arylsilane, (CH₃C₆H₄)SiH₃, as reactant. The process as disclosed generates toluene as a by-product and is thus claimed as a less hazardous alternative to the Keinan method which generates benzene from Phenyl-SiH₃.

U.S. Pat. No. 10,384,944 describes a halide exchange between, for example, LiI and SiH₂Cl₂, thereby generating LiCl and SiH₂I₂ in a Finkelstein-like reaction.

SUMMARY OF THE INVENTION

In summary, the invention provides certain complexes useful in the conversion of chloro- and bromo-silanes to highly-desired iodosilanes such as H₂SiI₂ and HSiI₃, via a halide exchange reaction. The species which mediates this reaction is an iodide reactant comprising aluminum. In certain embodiments, the iodide reactant comprising aluminum is a compound having the formula (A):

[M^(+q)]_(z)[Al(X)₃I_(w)]_(q)  (A),

wherein z is 0 or 1, w is 0 or 1, M is chosen from (i) Group 1 metal cations chosen from Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺, (ii) Group 2 metal cations chosen from Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺; and (iii) ammonium or C₁-C₆ alkyl or benzyl ammonium cations; q is the valence of M and is 1 or 2, and X is chloro, bromo, or iodo, provided that when z and w are zero, X is iodo.

Examples of such iodide reactants includes, for example, LiAl(I)₄, NaAl(I)₄, KAl(I)₄, Mg[Al(I)₄]₂, Ca[Al(I)₄]₂, LiAl(Cl)₃I, LiAlCl(I)₃, NaAl(Cl)₃I, NaAlCl(I)₃, KAl(Cl)₃I, KAlCl(I)₃, Mg[Al(Cl)₃I]₂, Mg[Al(Cl)(I)₃]₂, Ca[Al(Cl)₃I]₂, Ca[Al(Cl)(I)₃]₂, NH₄Al(I)₄, NH₄Al(Cl)₃I, NH₄Al(Cl)(I)₃, NaAl₂I₇, NaAl₃I₁₀, and Al(I)₃.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an ²⁷Al NMR spectrum of aluminates, of the form LiAl(I)_(x)(Cl)_(y), in solution during conversion of SiH₂Cl₂ to SiH₂I₂ using in situ generated aluminate reagent. The aluminate was generated by combining three equivalents each of AlCl₃ and LiI with respect to SiH₂Cl₂. The reaction was heated at 60° C. for 1 hour and NMR data was acquired. See Example 8 for further details.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the invention provides a method for preparing an iodosilane having the formula (I) or (II)

SiR_(x)I_(y)  (I), or

I_(y)R_(x)Si—SiR_(x)I_(y)  (II),

-   -   wherein x is 1, or 2, y is an integer of from 1 to 3, and         wherein the sum of x plus y is 4 in formula (I) and 3 in         formula (II) at each Si center, and wherein R is hydrogen or a         C₁-C₆ alkyl group;         which comprises contacting a halosilane having the formula

SiR_(x)D_(y) or D_(y)R_(x)Si—SiR_(x)D_(y),

-   -   wherein D is chloro or bromo,         with an iodide reactant comprising aluminum.

It should be appreciated that in this method, in order to form an iodosilane of formula (I), the halosilane reactant will necessarily be a compound of the formula SiR_(x)D_(y). Similarly, in order to form an iodosilane of formula (II), the halosilane reactant will be a compound of the formula: D_(y)R_(x)Si—SiR_(x)D_(y).

Exemplary iodosilanes as contemplated above include

SiHI₃,

SiH₂I₂,

SiH₃I,

SiH₂CH₃I,

SiH₂(CH₂CH₃)I,

SiH₂(CH₂CH₂CH₃)I,

SiH₂((CH₃)₂CH)I,

SiH₂(CH₂CH₂CH₂CH₃)I,

SiH₂((CH₃)₃C)I,

SiHCH₃I₂,

SiH(CH₂CH₃)I₂,

SiH(CH₂CH₂CH₃)I₂,

SiH((CH₃)₂CH)I₂,

SiH(CH₂CH₂CH₂CH₃)I₂,

SiH((CH₃)₃C)I₂,

SiCH₃I₃,

Si(CH₂CH₃)I₃,

Si(CH₂CH₂CH₃)I₃,

Si((CH₃)₂CF)I₃,

Si(CH₂CH₂CH₂CH₃)I₃,

Si((CH₃)₃C)I₃,

I₃Si—SiI₃.

I₂CH₃Si—SiCH₃I₂,

I₂(CH₃CH₂)Si—Si(CH₂CH₃)I₂,

I₂(CH₃CH₂CH₂)Si—Si(CH₂CH₂CH₃)I₂,

I₂((CH₃)₂CH)Si—Si((CH₃)₂CH)I₂,

I₂(CH₃CH₂CH₂CH₂)Si—Si(CH₂CH₂CH₂CH₃)I₂,

I₂((CH₃)₃C)Si—Si((CH₃)₃C)I₂,

ICH₃HSi—SiHCH₃I,

I(CH₂CH₃)HSi—SiH(CH₂CH₃)I,

I(CH₂CH₂CH₃)HSi—SiH(CH₂CH₂CH₃)I,

I((CH₃)₂CH)HSi—SiH((CH₃)₂CH)I,

I(CH₂CH₂CH₂CH₃)HSi—SiH(CH₂CH₂CH₂CH₃)I, and

I((CH₃)₃C)HSi—SiH((CH₃)₃C)I.

In one embodiment, the iodosilane of the formula (I) is H₂SiI₂.

In one embodiment, the iodide reactant comprising aluminum is a compound having the formula (A):

[M^(+q)]_(z)[Al(X)₃I_(w)]_(q)  (A),

wherein z is 0 or 1, w is 0 or 1, M is chosen from (i) Group 1 metal cations chosen from Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺, (ii) Group 2 metal cations chosen from Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺; and (iii) ammonium, C₁-C₆ alkyl ammonium, or benzyl ammonium cations; q is the valence of M and is 1 or 2, and X is chloro, bromo, or iodo, provided that when z and w are zero, X is iodo.

In one embodiment, M is chosen from cations such as (CH₃)₄N⁺, (CH₃CH₂)₄N⁺, (CH₃CH₂CH₂)₄N⁺, and (CH₃CH₂CH₂CH₂)₄N⁺.

In another embodiment, z is 1 and w is 1, depending on the valence of the cation, M. In such cases, the anionic portion of compounds of formula (A), i.e., [Al(X)₃I_(w)]_(q), can be referred to as aluminates and can be generated by reaction of the parent components in solution or in the solid state using 1:1 molar ratios of reactants (or 2:1 in the case of divalent Group 2 metal cations). By way of example, an LiAl(I)₄ aluminate can be prepared by mixing LiI and Al(I)₃ in solution or by reaction at high temperature when combined in a 1:1 molar ratio. The aluminates can be isolated easily from such reactions. The aluminates are isolable compounds and can thus be added to reaction mixtures to effect transformation of chloro- and bromosilanes to iodosilanes as described herein. Alternately, the above-mentioned aluminates can be prepared in situ and subsequently used for conversion of chloro- and bromosilanes to iodosilanes of formula (I) and (II) as set forth above. The properties and solid-state structure of the above described aluminates have been discussed in the literature by Braunstein (Braunstein, J. Advances in Molten Salt Chemistry, Volume 1, 1971) and Prömper and Frank (Prömper S. W. and Frank, W. Acta Cryst. 2017, E73, 1426).

Accordingly, in one embodiment, in the compounds of formula (A), z is 1, indicating “M” is present. Examples of compounds of the formula (A) wherein z is 1 include aluminates such as LiAl(I)₄, NaAl(I)₄, KAl(I)₄, Mg[Al(I)₄]₂, Ca[Al(I)₄]₂, LiAl(Cl)₃I, LiAlCl(I)₃, NaAl(Cl)₃I, NaAlCl(I)₃, KAl(Cl)₃I, KAlCl(I)₃, Mg[Al(Cl)₃I]₂, Mg[Al(Cl)(I)₃]₂, Ca[Al(Cl)₃I]₂, Ca[Al(Cl)(I)₃]₂, NH₄Al(I)₄, NH₄Al(Cl)₃I, NH₄Al(Cl)(I)₃, NaAl₂I₇, NaAl₃I₁₀, and the like.

In one embodiment, the iodide reactant comprising aluminum is aluminum triiodide (i.e., z and w are zero in formula (A)). In this regard, we have found that the displacement reaction occurs in the presence of aluminum triiodide alone; such aluminum triiodide can be used directly as the iodide reactant set forth herein or can be generated in situ by the reaction of aluminum metal with iodine. Al(I)₃ (and AlCl₃) are known to exist as tetrahedral based dimers but will be represented herein as monomeric species for the sake of simplicity.

Accordingly, in one embodiment, the invention provides a method for preparing a compound of the formula H₂SiI₂, which comprises contacting a compound of the formula H₂SiCl₂ with Al(I)₃. In another embodiment, the Al(I)₃ so utilized is generated in situ from elemental aluminum and iodine.

Additionally, Al(X)₃, when X is chloro, bromo, (or iodo) can be utilized in conjunction with a Group I or Group 2 iodide. In such cases, the aluminate species can be generated in situ by reacting, for example AlCl₃ with MgI₂, the latter of which can be formed in situ by the reaction of magnesium metal with iodine.

In these cases, multinuclear NMR analysis supports the hypothesis that the species formed is indeed an aluminate complex having the empirical formula M_(z)Al(X)₃I, as depicted above, which is believed to be the reactive species in this aluminum-mediated halogen displacement reaction. The aluminate species present in such reactions have been identified by ²⁷Al NMR spectroscopy. In a specific example SiH₂Cl₂ was treated with three equivalents of an aluminate reactant formed in situ from reaction of AlCl₃ and LiI. In this reaction SiH₂I₂ was generated with a 59% conversion as summarized in Example 8. The ²⁷Al NMR spectrum of the reaction mixture (FIG. 1) shows the aluminate species in the reaction responsible for the transformation of SiH₂Cl₂ to SiH₂I₂.

While not wishing to be bound by theory, we believe that this aluminate structure serves to mediate the displacement of the chlorine atoms on the silane to provide the desired iodosilanes.

In another embodiment, the iodide reactant is a compound of the formula MAl_(m)I_(n), wherein M is an alkali metal, and

(i) m is 2 and n is 7, or

(ii) m is 3 and n is 10.

In this embodiment, the iodide reactant can be a compound having the formula NaAl₂I₇ or NaAl₃I₁₀. These compounds may be prepared as taught in Boef, G.; Brins Slot, H.; Van Leeuwen, R. A. W.; Wessels, H.; Van Spronsen, Johannes W., Zeitschrift fuer Anorganische and Allgemeine Chemie (1967), 353(1-2), 93-102.

In general, aluminate species exist in the form wherein the aluminate anion is present as (AlX₄)⁻ and are synthesized by reaction of an aluminum halide, AlX₃, and a corresponding metal halide, M^(+q)I_(q), (wherein “q” represents valence of the metal cation, and the total number of anionic species necessary to provide an uncharged formula) in a 1:1 molar ratio for the Group 1 congeners. In these cases, the literature refers to the system as a 0.5:0.5/AlX₃:M^(+q)I_(q) system wherein the actual chemical species that exists is M^(+q)[AlX₄]_(q). Accordingly, and as an example, LiAl(I)₄ can be generated from reaction of equimolar amounts of LiI and Al(I)₃.

However, the above-mentioned aluminates can also exist when the reactants are combined in molar ratios that vary from the 1:1 example given. In these cases, the literature describes such systems as AlX₃:M^(+q)I_(q) systems that are either AlX₃ rich or M^(+q)I_(q) rich. The NaAl₂I₇ or NaAl₃I₁₀ compounds discussed above are examples where in both cases the systems are rich in Al(I)₃. An analogous situation also exists for the divalent Group 2 metal cation-based aluminates. In this embodiment of the invention the AlX₃ rich and the M^(+q)I_(q) rich variations of the iodide reactant can also mediate the transformation of halosilane to iodosilane when the AlX₃:M^(+v)I_(v) system is present in any ratios between 0.999:0.001 to 0.001:0.999.

In another embodiment, Al(X)₃ (X is chloro or iodo) can be utilized as a precursor for the conversion of chloro- and bromosilanes to iodosilanes. In this embodiment, equimolar mixtures of chloro- or bromosilane and M^(+q)I_(q) (q=oxidation state of M; e.g., MgI₂, q=⁺2) can be treated with 5-25 mol % of Al(X)₃. When so treated the chloro- or bromosilanes are converted to iodosilanes. In these cases, the AlX₃ and M^(+q)I_(q) react to form an aluminate species. In this regard, the reaction of Al(X)₃ with M^(+q)I_(q) need not be in a 1:1 stoichiometric proportion. The aluminate can mediate the transformation of chloro- or bromosilane to iodosilane and the needed Al—I functionality is regenerated by reaction between the aluminate and M^(+q) _(q). As described above, the iodide reactant comprising aluminum can be added to the reaction as discrete materials or generated in situ where possible.

Thus, in a further embodiment, the iodide reactant comprising aluminum is generated in situ from

a. AlX₃ and M^(+q)X_(q);

b. Al^(o), X₂, and M^(+q)X_(q);

c. AlX₃, M^(o), and X₂; or

d. Al^(o), M^(o), and X₂, wherein q represents the valence of M and X.

The methodology of the invention can be practiced neat or in the presence of an aprotic solvent which is non-reactive with the starting materials or iodosilane products. Such solvents include hydrocarbon solvents which are devoid of moieties such as oxygen, esters, carboxy groups, and ketones. Examples include benzene, toluene, hexane, cyclohexane, tetralin, decalin, mesitylene and the like.

The method for preparing the precursor compounds of the invention can be conducted in standard batch or continuous mode reactors. One of ordinary skill in the art would recognize the scale and type of reactors which could be utilized in the context of the reagents and products so produced.

Insofar as the methodology of the present invention generates neither iodine or hydrogen iodide, there is no need to utilize copper, antimony or silver compounds to stabilize the resulting iodosilane product. Additionally, in those cases where the iodide reactant does not comprise an alkali metal cation, such as is the case with Al(I)₃, ammonium iodide, or alkylammonium iodides, the resulting iodosilane product will thus necessarily also be free of alkali metal impurities. Accordingly, in a second aspect, the invention provides a precursor composition comprising a compound of the formula SiH₂I₂, having less than 1 ppm (parts per million) of antimony, silver, or copper impurities and less than about 1 ppm of sodium or lithium impurities. In a further aspect, the invention provides a precursor composition comprising a compound of the formula SiH₂I₂, having less than about 10 ppb (parts per billion) or less than about 5 ppb aluminum impurities.

Compounds of the formulae (I) and (II) are useful as precursors in the formation of silicon-containing films on the surface of a microelectronic device by methods such as atomic layer deposition. See for example, U.S. Pat. Nos. 10,580,645 and 10,424,477, incorporated herein by reference.

Compounds (I) and (II) can be introduced into a deposition chamber for the purposes of thermal CVD or ALD, or for the purposes of performing plasma-enhanced ALD or CVD. In these cases, a co-reactant gas can be introduced to deposit an SiO₂ film, via oxidation in an oxidizing environment with O₂, O₃, N₂O, or mixtures thereof. Similarly, compounds (I) and (II) can be introduced into a deposition chamber for the purposes of thermal CVD or ALD, or for the purposes of performing plasma-enhanced ALD or CVD. In these cases, a co-reactant gas can be introduced to deposit an SN film, via nitridation with N₂, NH₃, hydrazine or alkylhydrazine containing mixtures. The deposited films serve as dielectric layers within the microelectronic device.

EXAMPLES

This invention can be further illustrated by the following examples of certain embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated. All manipulations were carried out under inert atmosphere.

Example 1

To LiAl(I)₄ (0.13 g, 0.25 mmol) was added a solution of SiH₂Cl₂ in xylenes and benzene-d6 (0.025 g SiH₂Cl₂, 0.25 mmol SiH₂Cl₂, 1.0 ml benzene-d6, 0.075 g xylenes). The mixture was stirred at 60° C. for 45 minutes. The liquid was decanted from the solid ppt and placed in an NMR tube. Conversion of SiH₂Cl₂ to SiH₂I₂ was determined by analysis of the ¹H NMR spectrum of the reaction mixture. After 45 minutes of reaction time the distribution of reaction products was 92.4% SiH₂I₂ with 0.6% SiH₂Cl₂. There was also 7% of the monosubstituted product SiH₂(Cl)(I) in the reaction mixture as determined by ¹H NMR spectroscopy.

Example 2

To a solid mixture of Al(I)₃ (0.02 g, 0.05 mmol) and MgI₂ (0.275 g, 1.0 mmol) was added a solution of SiH₂Cl₂ in xylenes and benzene-d6 (0.10 g SiH₂Cl₂, 1.0 mmol SiH₂Cl₂, 1.0 ml benzene-d6, 0.30 g xylenes). The mixture was stirred for 50 minutes at 60° C. The liquid was decanted from the solid ppt and placed in an NMR tube. Conversion of SiH₂Cl₂ to SiH₂I₂ was determined by analysis of the ¹H NMR spectrum of the reaction mixture. After 50 minutes of reaction time the distribution of reaction products was 92.3% SiH₂I₂ with 0.7% SiH₂Cl₂. There was also 7% of the monosubstituted product SiH₂(Cl)(I) in the reaction mixture as determined by ¹H NMR spectroscopy.

Example 3

In situ generation of LiAl(I)₄: To a 3.0 ml quantity of benzened6 was added Al^(o) (0.050 g, 1.85 mmol), 12 (0.375 g, 1.5 mmol), and LiI (0.13 g, 1 mmol) to afford a dark red colored mixture. The mixture was stirred at 60° C. After one hour the initial red color of the mixture dissipated and gave a colorless mixture. To the in situ generated LiAl(I)₄ was added a solution of SiH₂Cl₂ in xylenes (0.10 g SiH₂Cl₂, 1.0 mmol SiH₂Cl₂, 0.30 g xylenes). The mixture was stirred at 60° C. Conversion of SiH₂Cl₂ to SiH₂I₂ was determined by analysis of the ¹H NMR spectrum of the reaction mixture. After 60 minutes of reaction time the distribution of reaction products was 90% SiH₂I₂ with 1% SiH₂Cl₂. There was also 8.6% of the monosubstituted product SiH₂(Cl)(I) in the reaction mixture as determined by ¹H NMR spectroscopy.

Example 4

In situ generation of Al(I)₃: To a 2.0 ml quantity of benzened6 was added Al^(o) (0.030 g, 1.1 mmol) and 12 (0.375 g, 1.5 mmol) to afford a dark red colored mixture. After stirring at 70° C. for 1.5 hours the color dissipated to afford a colorless mixture. To the in situ generated Al(I)₃ was added a solution of SiH₂Cl₂ in xylenes (0.025 g SiH₂Cl₂, 0.25 mmol SiH₂Cl₂, 0.075 g xylenes). The mixture was stirred at 60° C. for one hour. Conversion of SiH₂Cl₂ to SiH₂I₂ was determined by analysis of the ¹H NMR spectrum of the reaction mixture. After 60 minutes of reaction time the distribution of reaction products was 91% SiH₂I₂ with 0.5% SiH₂Cl₂. There was also 7% of the monosubstituted product SiH₂(Cl)(I) in the reaction mixture as determined by ¹H NMR spectroscopy.

Example 5

To Al(I)₃ (0.10 g, 0.25 mmol) was added a solution of SiH₂Cl₂ in xylenes and benzene-d6 (0.025 g SiH₂Cl₂, 0.25 mmol SiH₂Cl₂, 1.0 ml benzene-d6, 0.075 g xylenes). The mixture was stirred at 60° C. for 35 minutes. The mixture was placed in an NMR tube. Conversion of SiH₂Cl₂ to SiH₂I₂ was determined by analysis of the ¹H NMR spectrum of the reaction mixture. After 35 minutes of reaction time the distribution of reaction products was 79% SiH₂I₂ with 5% SiH₂Cl₂. There was also 16% of the monosubstituted product SiH₂(Cl)(I) in the reaction mixture as determined by ¹H NMR spectroscopy.

Example 6

To LiAl(I)₄ (0.40 g, 0.74 mmol) in 1.0 ml benzene-d6 was added SiHCl₃ (0.10 g SiHCl₃, 0.74 mmol SiHCl₃). The mixture was stirred at 60° C. for 45 minutes. The mixture was placed in an NMR tube and there was insoluble material present. Conversion of SiHCl₃ to SiHI₃ was determined by analysis of the ¹H NMR spectrum of the reaction mixture. After 45 minutes of reaction time the distribution of reaction products was 61% SiHI₃ with 23.3% SiHCl₃. There were also mixed ligand species present in the following amounts: 6.9% SiH(Cl)₂(I) and 8.8% SiH(Cl)(I)₂.

Example 7

A summary of reactions and conditions generating diiodosilane from dichorosilane with aluminate coreactants are presented in Table 1. The reactions were carried out by addition of one equivalent of dichlorosilane to two equivalents of the indicated, in situ generated, iodoaluminate under the conditions described. The percent conversion to diiodosilane was determined by analysis of ¹H NMR spectra of the reaction mixtures.

TABLE 1 Aluminate generated in situ from: 4 hours at 20° C. in toluene 4 hours at 20° C. in hexane AlX₃ MI H₂SiCl₂ H₂SiCll H₂SiI₂ HSiI₃ H₂SiCl₂ H₂SiClI H₂SiI₂ HSiI₃ AlCl₃ LiI 24.1% 27.5% 41.5% 0.0% 27.2% 29.2% 41.4% 0.0% AlCl₃ NaI 15.2% 27.2% 57.0% 0.0% 90.2% 6.4% 0.6% 0.0% AlCl₃ KI 55.6% 26.6% 17.1% 0.0% 97.8% 1.9% 0.0% 0.0% AlCl₃ NH₄I 42.3% 29.2% 28.6% 0.0% 99.8% 0.2% 0.0% 0.0% AlI₃ LiI 0.4% 4.4% 94.7% 0.0% 1.5% 9.3% 83.4% 5.6% AlI₃ NaI 0.7% 6.2% 90.0% 3.1% 3.1% 13.9% 80.0% 2.8% AlI₃ KI 1.1% 8.0% 80.1% 0.0% 4.8% 16.5% 75.5% 2.8% AlI₃ NH₄I 2.5% 12.2% 73.1% 0.0% 5.0% 16.4% 76.8% 1.5%

Example 8

A summary of reactions and conditions generating diiodosilane from dichorosilane with various reagents is presented in Table 2. The reactions were carried out by addition of a 25% dichlorosilane/xylene solution to the indicated iodide source in benzene-d6. The reaction time and temperatures are indicated and the percent conversion to diiodosilane was determined by ¹H NMR spectroscopy. The indicated equivalents (eq) of reagent used are with respect to using one equivalent of dichlorosilane in each reaction presented.

TABLE 2 Iodide source Al source H₂SiI₂ H₂Si(I)Cl H₂SiCI₂ HSiI₃ H₃Si(I) Temp Time (eq) (eq) (%) (%) (%) (%) (%) 60° C. 1 hr — AlI₃ (4) 83 12 4 2 0 60° C. 1 hr LiI(4) AlI₃ (4) 96 2.5 0 1.4 0.1 60° C. 35 min — A1(I)₃ (1) 79 16 5 0 0 60° C. 45 min (CH₃)₄NI (4) AlCI₃ (0.5) 20.5 28 51.5 0 0 70 C. 1.25 hr LiI (4) AlCI₃ (2) 83 14 3 0 0 60° C. 16 hr LiI (3) — 35 64 64 1 0.1 60° C. 16 hr (CH₃)₄NI (3) — 0 0 100 0 0 60° C. 1 hr LiI (3) AlCI₃ (3) 59 26 15 0.12 0.06 60° C. 2.5 hr CaI₂ (4) AlCI₃ (1) 73 19.5 7 0.36 0.31 60° C. 1.75 hr (Bu₄N)I (4) AlCl₃ (1) Obscured 27 73 obscured obscured 60° C. 1.5 hr CaI₂ (4) AlCI₃ (0.25) 63.5 24 12 0.13 0.10 60° C. 2 hr CaI₂ (4) — 0.3 5 94 0 0 60° C. 1 hr I₂ (6) Al⁰ (4) 91 7 0.5 1.6 0 60° C. 1.5 hr — Al⁰ (4) 0 0 100 0 0 60° C. 40 min LiAl(I)₃Cl (4) LiAl(I)₃Cl (4) 91 8 0.8 0.52 0.09 60° C. 45 min LiAlI₄ (1) LiAlI₄ (1) 92.4 7 0.6 0 0 60° C. 1 hr LiI (1) and Al⁰ (l) 90 8.6 1 0 0.4 I₂(1.5) 60° C. 1 hr MgI₂ (1) AlCl₃ (0.25) 94 5 1 0 0 60° C. 1 hr MgI₂ (1) 0 9.4 21.8 68.8 0 0 50 min 60° C. 1 hr MgI₂ (1) A1(I)₃ (0.15) 93.5 6 0.5 0 0 60° C. 50 min MgI₂ (1) A1(I)₃ (0.05) 92.3 7 0.7 0 0 60° C. 45 min MgI₂ (1) AlCl₃ (0.05) 87 11 2 0 0

Example 9

A summary of reaction conditions for conversion of trichlorsilane to triiodosilane using Al(I)₃ or aluminate reagents is presented in Table 3. Reactions were carried out in C₆D₆ at 100° C. in sealed containers for 16 hours. The percent distribution of silane products was determined by ¹H NMR spectroscopy. The indicated equivalents (eq) of reagent used are with respect to using one equivalent of dichlorosilane in each reaction.

TABLE 3 Al Iodide source (eq) source (eq) HSiI₃ HSiCl₂(I) HSiCl(I) HSiCI₃ Al(I)₃ (1) 0 53% 12%  20%  13% Al(I)₃ (3) 0 72% 6% 17%  3% Al(I)₃ (3) LiI (1) 87% 2% 10% 0.5% Al(I)₃ (3) LiI (2) 93% 0.5%   6% 0.2% Al(I)₃ (4) LiI (3) 93% 1%  7% 0.2% Al(I)₃ (3) LiI (2) 94% 0.5%   6% 0.1%

Example 10

A summary of reaction conditions for conversion of trichlorsilane to triiodosilane using various in situ generated aluminates is shown in Table 4 with relevant reaction conditions. An equimolar ratio of reactants was used and the percent conversion to the indicated silanes was determined by ¹H NMR spectroscopy.

TABLE 4 Aluminate generated 5.5 hours at 20° C. 23 hours at 20° C. in situ from: Solvent HSiCI₃ HSiCl₂I HSiClI₂ HSiI₃ HSiCI₃ HSiCl₂I HSiClI₂ HSiI₃ A1(I)₃ LiI Toluene 6.3% 4.6% 12.0% 77.2% 4.3% 4.2% 12.7% 78.8% A1(I)₃ LiI Hexane 23.5% 10.6% 15.2% 50.7 4.5% 7.6% 21.9% 66.0% A1(I)₃ NaI Toluene 7.5% 6.8% 16.0% 69.7% 7.0% 6.7% 16.4% 69.9% A1(I)₃ NaI Hexane 8.5% 10.1% 16.9% 64.5% 4.2% 6.4% 17.2% 72.2% A1(I)₃ KI Toluene 2.6% 2.6% 10.6% 84.2% 2.3% 2.3% 10.0% 85.5% A1(I)₃ KI hexane 18.8% 10.0% 16.7% 54.4% 6.7% 6.8% 16.2% 70.3%

Example 11

A summary of reaction parameters for the conversion of trichlorsilane to triiodosilane using MgI₂, CaI₂, ZnI₂, and AlI₃ as the ‘sole’ reactants in solution. The indicated percent conversions were determined by ¹H NMR spectroscopy. The indicated equivalents (eq) of iodine-containing reagent used are relative to using one equivalent of dichlorosilane in each reaction. Only AlI₃ reagent yields SiHI₃ under these reaction conditions.

TABLE 5 5 hours at 60° C. Solvent Reagent (eq) HSiI₃ HSiCl₂I HSiClI₂ HSiCI₃ Toluene MgI₂ (1.5) 0 4.5%  0 95.5%  Hexane MgI₂ (1.5) 0  3% 0 97% Toluene CaI₂ (1.5) 0 0 0 100%  Hexane CaI₂ (1.5) 0 0 0 100%  Toluene ZnI₂ (1.5) 0 0 0 88% Hexane ZnI₂ (1.5) 0 0 0 99% Toluene AlI₃ (1.0) 60% 10% 19% 11% hexane AlI₃ (1.0) 53% 13% 19% 15%

Example 12

In a typical procedure used to generate SiH₂I₂ iodine (335 grams, 1.32 mol) was charged into a flask and toluene was added to make a concentrated solution. To a separate flask was charged aluminum (25 grams, 0.926 mol, 20-40 mesh) and toluene was added to make a slurry. At an internal temperature of 45° C. the iodine solution was slowly added to the aluminum over 3 hours, maintaining an internal temperature of 45-55° C. The residual undissolved iodine was dissolved in toluene and charged into the reaction mixture repeatedly until no iodine remained. After the complete addition of iodine, the reaction mixture was stirred at 45-50° C. for 2 hours, followed by stirring for 12 hours at room temperature. The volatiles were removed in vacuo at 40° C. to leave a concentrated mixture. Hexanes were added to the mixture to further precipitate the solid Al(I)₃. The solid Al(I)₃ was rinsed with hexanes twice and resuspended in hexanes to give an Al(I)₃ suspension. To the Al(I)₃ suspension was added SiH₂Cl₂ (135 grams, 1.33 mol) over 5 minutes. The reaction mixture was stirred at 20° C. for 1 hour, and then was heated to 35° C. for 3 hours. The reaction mixture was cooled to 20° C. and filtered. The solids were rinsed three times with hexanes and the filtrates were combined. The filtrate was analyzed and revealed 75% conversion to SiH₂I₂. The volatiles were removed in a distillation system at 50-300 torr and an internal temperature of 35-50° C. The product was distilled at 45-50° C. at 8-20 Torr to afford 192 grams of SiH₂I₂ in 52% yield.

The invention has been described in detail with particular reference to certain embodiments thereof, but it will be understood that variations and modifications can be affected within the spirit and scope of the invention. Having thus described several illustrative embodiments of the present disclosure, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the disclosure covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the disclosure. The disclosure's scope is, of course, defined in the language in which the appended claims are expressed 

1. A method for preparing an iodosilane having the formula (I) or (II) SiR_(x)I_(y)  (I), or I_(y)R_(x)Si—SiR_(x)I_(y)  (II), wherein x is 1, or 2, y is an integer of from 1 to 3, and wherein the sum of x plus y is 4 in formula (I) and 3 in formula (II) at each Si center, and wherein R is hydrogen or a C₁-C₆ alkyl group; which comprises contacting a halosilane having the formula SiR_(x)D_(y) or D_(y)R_(x)Si—SiR_(x)D_(y), wherein D is chloro or bromo, with an iodide reactant comprising aluminum.
 2. The method of claim 1, wherein y is
 2. 3. The method of claim 1, wherein the iodide reactant comprising aluminum is a compound having the formula (A): [M^(+q)]_(z)[Al(X)₃I_(w)]_(q)  (A), wherein z is 0 or 1, w is 0 or 1, M is chosen from (i) Group 1 metal cations chosen from Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺, (ii) Group 2 metal cations chosen from Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺; and (iii) ammonium, C₁-C₆ alkyl, or benzyl ammonium cations; q is the valence of M and is 1 or 2, and X is chloro, bromo, or iodo, provided that when z and w are zero, X is iodo.
 4. The method of claim 3, wherein z is 1 and w is
 1. 5. The method of claim 4, wherein M is Li⁺ or Na⁺.
 6. The method of claim 4, wherein M is chosen from NH₄ ⁺, (CH₃)₄N⁺, (CH₃CH₂)₄N⁺, (CH₃CH₂CH₂)₄N⁺, and (CH₃CH₂CH₂CH₂)₄N⁺.
 7. The method of claim 3 wherein M is Mg⁺² or Ca⁺².
 8. The method of claim 1, wherein the iodide reactant comprising aluminum is aluminum triiodide.
 9. The method of claim 8, wherein the aluminum triiodide is generated in situ from aluminum metal and iodine.
 10. The method of claim 3, wherein the compound of formula (A) is chosen from LiAl(I)₄, NaAl(I)₄, KAl(I)₄, Mg[Al(I)₄]₂, Ca[Al(I)₄]₂, LiAl(Cl)₃I, LiAlCl(I)₃, NaAl(Cl)₃I, NaAlCl(I)₃, KAl(Cl)₃I, KAlCl(I)₃, Mg[Al(Cl)₃I]₂, Mg[Al(Cl)(I)₃]₂, Ca[Al(Cl)₃I]₂, Ca[Al(Cl)(I)₃]₂, NH₄Al(I)₄, NH₄Al(Cl)₃I, NH₄Al(Cl)(I)₃, NaAl₂I₇, NaAl₃I₁₀, and Al(I)₃.
 11. The method of claim 1, wherein the iodide reactant comprising aluminum is a compound of the formula MAl_(m)I_(n), wherein M is an alkali metal, and m is 2 and n is 7, or m is 3 and n is
 10. 12. The method of claim 11, wherein the iodide reactant is a compound of the formula NaAl₂I₇.
 13. The method of claim 11, wherein the iodide reactant is a compound of the formula NaAl₃I₁₀.
 14. The method of claim 3, wherein the iodide reactant comprising aluminum is generated in situ from a. AlX₃ and M^(+q)X_(q); b. Al^(o), X₂, and M^(+q)X_(q); c. AlX₃, M^(o), and X₂; or d. Al^(o), M^(o), and X₂, wherein q represents the valence of M.
 15. The method of claim 1, wherein the compound of formula (I) is chosen from SiHI₃, SiH₂I₂, SiH₃I, SiH₂CH₃I, SiH₂(CH₂CH₃)I, SiH₂(CH₂CH₂CH₃)I, SiH₂((CH₃)₂CH)I, SiH₂(CH₂CH₂CH₂CH₃)I, SiH₂((CH₃)₃C)I, SiHCH₃I₂, SiH(CH₂CH₃)I₂, SiH(CH₂CH₂CH₃)I₂, SiH((CH₃)₂CH)I₂, SiH(CH₂CH₂CH₂CH₃)I₂, SiH((CH₃)₃C)I₂, SiCH₃I₃, Si(CH₂CH₃)I₃, Si(CH₂CH₂CH₃)I₃, Si((CH₃)₂CH)I₃, Si(CH₂CH₂CH₂CH₃)I₃, Si((CH₃)₃C)I₃, I₃Si—SiI₃. I₂CH₃Si—SiCH₃I₂, I₂(CH₃CH₂)Si—Si(CH₂CH₃)I₂, I₂(CH₃CH₂CH₂)Si—Si(CH₂CH₂CH₃)I₂, I₂((CH₃)₂CH)Si—Si((CH₃)₂CH)I₂, I₂(CH₃CH₂CH₂CH₂)Si—Si(CH₂CH₂CH₂CH₃)I₂, I₂((CH₃)₃C)Si—Si((CH₃)₃C)I₂, ICH₃HSi—SiHCH₃I, I(CH₂CH₃)HSi—SiH(CH₂CH₃)I, I(CH₂CH₂CH₃)HSi—SiH(CH₂CH₂CH₃)I, I((CH₃)₂CH)HSi—SiH((CH₃)₂CH)I, I(CH₂CH₂CH₂CH₃)HSi—SiH(CH₂CH₂CH₂CH₃)I, and I((CH₃)₃C)HSi—SiH((CH₃)₃C)I.
 16. The method of claim 1, wherein the compound of formula (I) is H₂SiI₂.
 17. The method of claim 16, wherein the iodide reactant comprising aluminum is Al(I)₃.
 18. The compound of claim 1, wherein the compound of formula (I) is HSiI₃.
 19. A precursor composition comprising a compound of the formula SiH₂I₂, having less than 1 ppm of antimony, silver, or copper impurities and less than about 1 ppm of sodium or lithium impurities.
 20. A precursor composition comprising a compound of the formula SiH₂I₂, having less than about 10 ppb (parts per billion) of aluminum impurities. 